I would take it to mean neither. That article doesn't specify, but it
could mean someone who inspects tickets on a bus where all passengers
are already required to hold them as a "revenue protection" exercise.
These people are not officially called "bus inspectors". The other, and
more probaby more accurate, meaning is an official who observes buses
at a fixed point on a route to regulate the service on behalf of the
bus company and ensure drivers aree keeping to time etc. In London,
both TfL and the bus operating companies employ such officials.